From a strict theoretical point of view there is no real reason to expect any diffence between nylon, bone or Ivorit bridge pins.You can challenge everybody who has a strong opinion about this to tell these materials apart in a blind test. Brass pins, however, do have a distinct influence on the tonal properties that can be explained by their greater mass adding to the inertia of the swinging bridge, both softening the attack and increasing sustain.

In theory, because plastic pins are the lightest, plastic pins should increase the responsiveness of the guitar the most, but in practice it doesn’t. The reason is that the softer material makes it easy to string the guitar incorrectly. Stringing the guitar incorrectly is the ultimate tone killer and I would say that well over 80% of the people I meat string their guitar the wrong way. So harder materials like bone and wood will do a bit more to force you to string your guitar up right and they are still light enough to not have a noticeable deadening factor on your guitar. Wood and bone are still soft enough that if you don’t try to string up right, you can still string up wrong, ruining your pins and killing your tone, but if you know what you are doing, they are hard enough that you won’t accidentally string up wrong. Brass pins, IMO, are too heavy. They significantly decrease the guitars responsiveness, and slightly decrease the guitars volume. The increase in sustain does not outweigh the other side effect.